1. Field of the Invention
The present invention is related to the field of digital image processing, and more specifically to processing of a decompressed digital image to remove color bleeding artifacts by filtering at the chrominance plane.
2. Description of the Related Art
When images are stored in arrays of pixels, each pixel stores a small portion of an image, in the form of image data. The same is true for both static images (such as photographs), and for video sequences.
The large volume of image data slows down its transmission. To alleviate the problem, compression techniques are used to reduce the amount of data. The image is afterwards decompressed and reconstructed.
A problem arises when a high compression technique is used with insufficient bit rate of transmission. When the image is reconstructed, it includes visual noise. The noise is the appearance of artifacts, such as color bleeding artifacts and ringing artifacts.
Color bleeding artifacts appear as color of one region smearing (or xe2x80x9cbleedingxe2x80x9d) onto a neighboring region. These artifacts appear in areas where large quantization errors were introduced by the initial compression. This happens where compression was difficult, such as scenes with a lot of motion and/or high spatial frequency contents.
Artifacts are usually removed by post processing of the decompressed image. Algorithms process the image data, to produce a processed image. Such algorithms have limitations. Unlike with ringing artifacts, intensive processing is required to remove color bleeding artifacts. If the data is overprocessed, however, then the image information starts being oversmoothed, which detracts from the overall image quality.
The present invention overcomes these problems and limitations of the prior art. The present invention notices that color bleeding artifacts become perceptually objectionable when the bleeding color has a color hue different from its surrounding area. The invention emphasizes more aggressive filtering at the chrominance plane than at the luminance plane, for eliminating the objectionable effect of color bleeding. The invention works well because the human eye is less sensitive to the details of the chrominance information than to those of the luminance information.
Generally, the present invention provides a method and a system for processing a decompressed video image. A video frame is decomposed into groups of pixels, such as blocks. Blocks that contain moving edges are preferably not processed further. The remaining blocks are preferably examined for the likelihood of having color bleeding artifacts, and not processed further if the likelihood is low. The remaining blocks are de-color bleeding filtered at the chrominance plane, without affecting the luminance plane.
The invention thus removes color bleeding artifacts, while not sacrificing much image information (which is mostly stored in the luminance component). The invention is additionally computationally fast. Since it obviates the need for over applying other, computationally intense post processing techniques, the invention becomes a prime choice for image post processing after decompression.
The invention will become more readily apparent from the following Detailed Description, which proceeds with reference to the drawings, in which: